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Issue 04/2015

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Foam Sandwich panel from

Foam Sandwich panel from wood and bioplastics By: Hendrik Roch Fraunhofer UMSICHT, Oberhausen, Germany Dr. Jan Lüdtke Thünen-Institut für Holzforschung, Hamburg, Germany Figure 1: Sandwich panels are usually used in lightweight construction Figure 2: Granules containing gas before and after foaming Figure 3: Foamed samples from biobased plastics (left) and fossilbased reference (right) Wood is a sought-after raw material for energy generation as well as for material utilization. One of the major consumers is the wood-based panels industry, producing for example particleboard for furniture manufacturing and interior housing work. A new form of wood-based sandwich panels consists of a hybrid structure with a lightweight foamed core layer and particleboard cover layers, still creating a strong structure. At present, the core consists of plastics from fossil resources. Fraunhofer UMSICHT (Oberhausen, Germany) together with Thünen Institute for Wood Research (Hamburg, Germany) is now developing a novel sandwich panel based on renewable materials. For the production of the sandwich panel a continuous process was developed by the wood researchers. Plastic granules, loaded with a blowing agent, are scattered on a bottom layer of agglutinated wood particles. Then, a second layer of agglutinated wood particles is spread on top. By heat and pressure the cover layers are compacted and the adhesive cures. In parallel, the polymer phase softens, followed by the activation of the blowing agent. To allow for the expansion of the polymer foam, the hot press opens to a predefined distance. The lightweight foam core is formed and simultaneously bonds to the facings forming a three layered sandwich panel. In future without fossil resources? The research teams of Fraunhofer UMSICHT and Thünen Institute for Wood Research have adapted this process to a new bioplastic. “The use of the new innovative lightweight construction material based on natural resources allows the complete substitution of fossil based polystyrene in sandwich panels”, explained Hendrik Roch from the department Bio-based Plastics at Fraunhofer UMSICHT. As a result of the first trials at Fraunhofer UMSICHT i. e. the combination of cellulose acetate butyrate (CAB) with a citrate plasticizer (a promising substitute for harmful phthalic acid based plasticizer) turn out as a promising formulation. Thus, a bioplastic compound with a melting temperature of 110 °C, similar to polystyrene (PS), can be achieved. As an exemplary result of the material development table 1 shows a comparison of the material properties of PS and CAB with plasticizer. The comparison demonstrates higher stiffness and strength of PS against plasticized CAB, but the latter reveals better elongation properties and double to triple impact strength. These are good conditions for the foamability of the material. Parallel to the material development, the basic expansion properties of the material, depending on 36 bioplastics MAGAZINE [04/15] Vol. 10

Foam pressure, temperature and blowing agents, are tested. First trials to produce expandable bioplastics beads in a process similar to EPS production were successful. The basic material (compound) is mixed in an extruder with the blowing agent. The granules containing blowing agent are tested regarding their foamability. In a mould tool water vapour heats the granules, with the result that the gas in the granules expands. A light, foamed and stable core structure from bioplastics is produced, fused to a moulded part in a closed aluminum mould. After cooling, the finished part is ejected from the mould. Process optimizing Followed by the material development and foaming trials the production of the final biobased sandwich panels is tested at Thünen Institute for Wood Research. The aim is the production of a highly compressed facing, which achieves the best possible bonding to the core. Therefore, the process (considering core layer granules, material moisture, adhesive type and amount, pressing time and power, etc.) has to be developed in such a way, that an optimized formation of facing and boundary layer occurs. Next steps in the project will be the optimization of the new products to substitute EPS without changing the processing parameters. Additionally, the researchers will further improve the material properties concerning temperature resistance, strength, etc. Polystyrene · CAB/Pl. Density 1,040 kg/m 3 1,180 kg/m³ E-Modulus 3,000 – 3,600 MPa 1,000 – 1,100 MPa Tensile strength 46 – 60 MPa 24 MPa Elongation at break 3 – 4 % 14 % Charpy notched impact strength 2 – 5 kJ/m 2 8.9 kJ/m 2 Glass transition temperature 60 – 100 °C 110 – 140 °C Biodegradability No Yes Table 1: Comparison of the material properties of unexpanded PS and plasticized CAB Table 2: Comparison of material and energy input for 1 cubic meter of typical particleboards and sandwich materials Particleboard (650 kg/m 3 ) Sandwich hybridpanel (370 kg/m 3 ) Wood 570 kg/m 3 280 kg/m 3 Resin & additives 80 kg/m 3 45 kg/m 3 Polymer - 45 kg/m 3 Energy (thermal & electrical) 100 % ~ 50 % Material and energy demand during production A parallel, critical observation by means of life cycle analysis (LCA) evaluates the product and eventually adjusts the project. Table 2 shows a comparison of material and energy demand during production between a standard particleboard and a sandwich hybrid-panel. Sandwich panel economics The panel price strongly depends on the application in which the sandwich construction is to be used. While particleboard is a rather low cost and low value standard product, substitute products gain a considerable benefit if they can be adapted to special applications where dedicated features (e. g. low weight, embedded thermal and sound insulation etc.) provide an added value to the customer. As the facing particles are exchangeable with fibres, strands or other types of particular material a great variety of products can be achieved. All types of hybridpanels comprise the one or the other special feature, so that they will be able to compete in these niche markets against the cheaper standard particleboard. Funding The research project “Material and process development for the production of a wood bioplastics sandwich panel based on renewable resources” is funded by the Forest Climate Fund, jointly coordinated by the Federal Ministry of Agriculture (BMEL) and the Federal Ministry of the Environment (BMUB). Project management agency is the Federal Office for Agriculture and Food (BLE), funding code 28WB304002. Your reliable partner in plastics BÖSEL PLASTIC MANAGEMENT Bösel Plastic Management GmbH has been known as a reliable partner in plastic industry for more than 20 years. Our high-quality regrinds, regranulates and compounds represent economical material handling. Innovative solutions and highest quality with best value for money convince our customers. The approach „from product to product“ closes the material cycle. We offer: production + sale of regrinds, regranulates and compounds grinding und granulating composite separation innovative solutions and consulting bioplastics (PLA) Feel free to contact us! Bösel Plastic Management GmbH Industriestr. 20-24 • 26219 Bösel • Tel.: 04494 1555 • Fax: 04494 8327 E-Mail: • bioplastics MAGAZINE [04/15] Vol. 10 37

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